Future data storage devices such as optical data storage media and magnetic data storage media are expected to continue to utilize greater data densities. As a result, electron beam (e-beam) lithography is increasingly used in the fabrication of optical and magnetic data storage media.
As an example, optical data storage devices use a master disk from which the optical data disks are replicated. In one manufacturing method, a substrate is placed in an e-beam lithography apparatus and patterned to create a relief pattern in the substrate. A daughter disk is created from the master disk by electroplating a metal layer upon the master disk to capture a negative image the relief pattern formed on the master disk. The metal layer is then removed and the actual optical data storage disks are made by melting or pressing polycarbonate pellets to replicate the relief pattern of the master disk. Thus, one master disk can be used to create many daughter disks which are in turn used to create many optical data storage disks.
In the past, e-beam, or laser beam, lithography utilized precision mechanical positioning to position a substrate beneath an electron beam column 110 which focuses and aligns the electron beam used to pattern a substrate. As the need for greater precision became apparent, in order to support greater data density on the substrate, laser interferometers were used to more precisely position the substrate beneath the electron beam column.
FIG. 1 shows a conventional e-beam lithography apparatus 100. In FIG. 1, a substrate 101 is disposed upon a stage 105. Stage 105 is rotated by a spindle 106 which is in turn mounted on a linear actuator 107. A mirror 108 is used to detect the positioning of linear actuator 107 using a laser interferometer 120. As a result, the position of stage 105 and substrate 101 can also be determined precisely. In a rotary stage e-beam lithography apparatus, spindle 106 comprises a mirrored surface which is used to detect the positioning of spindle 106 using one or more laser interferometers 130. Thus, mirror 108 can determine the position of linear actuator 107 in an X plane of movement while one or more other mirrors (not shown) can determine the position of linear actuator 107 in Y and Z planes of movement. Additionally, laser interferometer 120 can detect wobble of spindle 106 around its axis of rotation. Thus, the positioning of stage 105 can be determined very precisely and used to control the positioning of substrate 101 with respect to electron beam column 110. However, due to the trend toward increased data density used in data storage devices, conventional e-beam lithography positioning methods may not have sufficient precision to pattern data storage substrates. This transition when the e-beam lithographic tool may be insufficient occurs at track densities larger than 300 ktpi (thousands tracks per inch).